This invention relates to a navigation system which is operated to compute an optimum route from a starting point intersection to a destination Intersection and guide a vehicle along this optimum route.
In a navigation system disclosed in Japanese. Laid-Open Patent Application No. 173299/89 (U.S. Pat. No. 4,937,753), when a starting point and a destination are inputted, one of the intersections near the starting point is determined as a starting point intersection and one of the intersections near the destination is determined as a destination intersection. Then, an optimum route from the starting point to the destination via the starting point intersection and the destination intersection is computed. When running, the vehicle is guided along the optimum route. In this navigation system, it is necessary to input data as to where the starting point is and where the destination is in detail and correctly. However, the driver sometimes does not remember the starting point and destination In detail. In this case, since it is practically impossible to input the starting point and destination, the navigation system is not useful.
In the above-mentioned Laid-Open Application, there is disclosed, as the prior art, a navigation system in which the starting point intersection and the destination intersection are inputted directly. However, there is no specific description on how to input the starting point intersection and the destination intersection.
In a navigation system discussed in Japanese Laid-Open Patent Application No. 51000/87, many district names are indicated on many touch keys displayed on a screen of a display unit (FIG. 12) when the screen is in a destination input mode. The driver touches some of the touch keys with his fingers to select the name of a district where the destination exists. Upon selection, as shown in FIG. 13, a map of the selected district is displayed on the screen of the display unit but in many divided sections. The driver selects, through the touch keys, one of the divided sections where the destination exists. Upon selection, the map of the selected section is enlarged and displayed on the screen but in further narrowly divided sections as shown in FIG. 14. Among them, the driver selects one section (one of the narrowly divided sections) where the destination exists, through the touch keys. When the narrowly divided section (or district) where the destination exists is selected, the destination intersection existing in this narrowly divided section is determined. In the same procedure, a narrowly divided section (or district) where the starting point exists is selected and the starting point intersection is determined. Then, an optimum route between the starting point intersection and the destination intersection is computed. In this navigation system, unless the driver knows the map of the starting point and destination well, the optimum route cannot be computed. In this navigation system, it is possible to display a list of names of famous facilities (FIG. 15) by turning ON a touch key indicating "LIST" when the screen is in the mode of FIG. 14, and therefore one of the names of facilities can be inputted as the destination. However, if the destination is not a famous facility and therefore not included in the list, the optimum route cannot be computed.
In another navigation system disclosed by Japanese Laid-Open Patent Application No. 271110/88, a list of city names is displayed first on the screen of the display unit. When one of the city names is selected through a touch key. the names of small administrative districts such as towns, etc. which exist in the selected city are listed on the display screen. When one of the small administrative districts is selected through the touch key, even smaller administrative districts than the first-mentioned small administrative district are listed. In this way, tile destination can be determined by several touch key operations made by the driver on the screen of tile display unit. However, in this system, it is necessary for the driver to remember the names of small administrative districts.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a navigation system for use in a vehicle which can compute an optimum route based on a road name comparatively clearly remembered by the driver even if the driver does not remember the starting point and/or the destination clearly and in detail.
According to the present invention, there is provided a navigation system comprising:
(a) map information storage means for storing intersections, a net of roads, and administrative districts;
(b) administrative district input means for inputting a name of an administrative district;
(c) first road input means for inputting a name of a first road;
(d) second road input means for inputting a name of second road;
(e) intersection determination means for determining an intersection formed by such inputted first and second roads in the inputted administrative district; and
(f) optimum route computation means for computing an optimum route from a starting point intersection to a destination intersection, at least one of the starting point intersection and the destination intersection being the intersection determined by the intersection determination means.